Thiiranes

Thiiranes (episulfides) have been suggested as intermediates in the reaction of thionyl chloride with various substrates including ketones and carboxylic acids.54 However, apart from one claim, later corrected, no such compounds have been isolated.55,56 

These sulphur analogs of the 1,2-epoxides are variously known by the names thiiranes, thiacyclopropanes, alkylene sulphides, and episulphides. They are known to polymerize by the three catalytic mechanisms discussed for the oxygen compounds. Thus the same divisions are possible. For a discussion of some of the mechanistic aspects of these polymerizations as compared to epoxides, the reader is referred to a recent paper by Vandenberg [35]. 

The anionic polymerization of thiiranes appears to proceed very clearly and in a well defined manner. Living systems have been found and good kinetic measurements have been possible [36]. The base catalysed polymerization of ethylene sulphide (ES) was probably one of the earliest thiirane polymerizations noted. However, the studies have been hindered because the polymer formed is highly crystalline and insoluble. Homogeneous solution studies have not been possible. Propene sulphide (PS) on the other hand gives soluble amorphous polymer and has been amenable to careful study. Indeed the formation of amorphous polypropene sulphide is the major evidence that base catalysed polymerization is ionic and proceeds by the reactions indicated by the equations 

The transfer reaction observed in the base catalysed polymerizations of PO does not occur with the sulphide analog and high molecular weight polymers are observed. In fact, under conditions of high purity [37] no termination reactions were observed and the polymerization had all the characteristics of a living system. The relationship 

The presence of free naphthalene was demonstrated [38]. However, the scheme did not explain all the experimental data. 

A kinetic study of this sodium naphthalene initiated polymerization of PS was made by Sigwalt et al. [39]. Low molecular weight living polymer was used in order to circumvent the problem of an observed induction period. If the concentration of living ends [C] was 10 mole 1 , the kinetics followed the equation 

The IR and VCD speara of (2jR)-methylthiirane 11 vrere studied - 0 by both MFP and VCT methods. The experimental VCD spectra of 11 were measured early in 19871° and again in 1991.it as first studied theoretically in 1988 by the MFP method with both the CO and the DO gauges. In this study, the wavefunction derivatives were obtained using a numerical differentiation method, a corrected theoretical geometry, a scaled force field, and a 6-31G basis set. Comparison with experimenti indicated that the simulated VCD spectrum in the CO gauge at the center of mass bears a closer resemblance to the experimental VCD spectrum. 

As the first VCD study partially at the MP2 level of theory, Amos et al. studied the VCD of 11 using the MFP method with the force field and APTs at the MP2 level, and AATs at the SCF level.The equilibrium geometries and force fields were obtained with a variety of basis sets, and only the results obtained with a DZP basis set were quoted. The authors concluded that the correlation effects improve both the APTs and frequencies, and that correlation affected frequencies more than intensities in the C-H stretching region. 

Molecule 11 was also studied by the VCT/SCF/6-31G 3) ap-proach, in which all properties were obtained at the SCF/6-31G - level. The calculated signs of all rotatory strengths correctly reproduce the available experimental rotatory strengthsi by both the VCT-CO and the VCT-DO approaches. 

The experimental and theoretical IR and VCD spectra of the dimethyl substituted thiiranes, namely (2jR,3jR)-dimethylthiirane 12 and (2R,3R)-dimethylthiirane-2,3-d2 13 have been reported. The VCT method with the 6-31G - ) basis set was used in those studies. All properties vrere obtained 

Rgure 2 Theoretically simulated, Lorentzian iineshape of 5 cm half width at half height, and experimental (CCI4) VCD and IR spectra of (2R.3R)-dimethyIthiirane 12 in the region 700-1600 cm (Reference 101). SCF frequencies are scaled by 0.9. 

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The problem of the synthesis of highly substituted olefins from ketones according to this principle was solved by D.H.R. Barton. The ketones are first connected to azines by hydrazine and secondly treated with hydrogen sulfide to yield 1,3,4-thiadiazolidines. In this heterocycle the substituents of the prospective olefin are too far from each other to produce problems. Mild oxidation of the hydrazine nitrogens produces d -l,3,4-thiadiazolines. The decisive step of carbon-carbon bond formation is achieved in a thermal reaction a nitrogen molecule is cleaved off and the biradical formed recombines immediately since its two reactive centers are hold together by the sulfur atom. The thiirane (episulfide) can be finally desulfurized by phosphines or phosphites, and the desired olefin is formed. With very large substituents the 1,3,4-thiadiazolidines do not form with hydrazine. In such cases, however, direct thiadiazoline formation from thiones and diazo compounds is often possible, or a thermal reaction between alkylideneazinophosphoranes and thiones may be successful (D.H.R. Barton, 1972, 1974, 1975). 

Photolysis of 4-aminothiazolium salts in aqueous solution may cause ring opening, probably via a thiirane. to give a-cyano-jS-aminovinyl-disulfide or a-acylacetamidine derivatives (22). 

Methylthio)cyclopentane Thiirane Cyclopentyl methyl sulfide... 

The facility with which oxiranes may be prepared and the ease with which they undergo ring opening with nucleophiles or electrophiles makes them useful synthons. Aziridines and especially thiiranes have been less widely exploited in this respect. 

Thiiranes can be made from nascent sulfur , such as is obtained by the thermolysis of diethyl tetrasulfide (64HC(l9-l)59l). 

Three-membered rings containing one sulfur atom are named as thiiranes (1) or thiirenes... 

Table 1 Bond Lengths and Angles for some Thiiranes and Thiirenes...

The configurations of chiral thiiranes and thiirane 1-oxides can be determined by H NMR experiments in chiral solvents such as (R)-(-)- -phenyl-2,2,2-trifluoroethanol. The... 

Chemical shifts ( H, C) and coupling constants for some thiiranes and thiirenes are given in Table 2. The shifts of substituted derivatives may be calculated by the use of additivity relationships found in textbooks on NMR. 

The H NMR spectrum of thiirane 1-oxide is complex (AA BB ) at 60 MHz 24 lines are cfbserved consisting of two sets of 12 centered about a midpoint. The H NMR chemical shift in thiirane 1,1-dioxide is fairly sensitive to solvent variations partly because of the high dipole moment (4.4 D) of the sulfone. The benzene-induced shift, A5 (CeDe-CCLt), is large (-1.04 p.p.m.), as expected from the presence of a sulfone group. Oxygen-17 chemical shifts for thiirane 1-oxide and thiirane 1,1-oxide are -71 and +111 p.p.m. respectively, relative to H2O. 

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